--- a/tests/makefile
+++ b/tests/makefile
@@ -104,10 +104,10 @@ giffilter-regress:
 
 giffix-rebuild:
 	@echo "Rebuilding giffix test."
-	@head --bytes=-20 <$(PICS)/treescap.gif | $(UTILS)/giffix 2>/dev/null | $(UTILS)/gifbuild -d >giffixed.ico
+	@bsz=`stat -f %z $(PICS)/treescap.gif`; head --bytes=$$(($$bsz - 20)) <$(PICS)/treescap.gif | $(UTILS)/giffix 2>/dev/null | $(UTILS)/gifbuild -d >giffixed.ico
 giffix-regress:
 	@echo "giffix: Testing giffix behavior"
-	@head --bytes=-20 <$(PICS)/treescap.gif | $(UTILS)/giffix 2>/dev/null | $(UTILS)/gifbuild -d | diff -u giffixed.ico -
+	@bsz=`stat -f %z $(PICS)/treescap.gif`; head --bytes=$$(($$bsz - 20)) <$(PICS)/treescap.gif | $(UTILS)/giffix 2>/dev/null | $(UTILS)/gifbuild -d | diff -u giffixed.ico -
 
 gifinto-regress:
 	@echo "gifinto: Checking behavior on short files."
